Limit the range of the missionary's full action but increase its effectivnes.
The missionary could only really be used unthreatened over multiple turns.
Since any unit can be disbanded during upkeep before it is evangelized, the missionary is only a slow destroy effect.
Now it is way more potent controlling cheaper units with the first action but it has to be close to the enemy unit making it more vulnerable.

This allows to not use the internal game state directly from client
code.

This is done to propagate the chosen variadic play cost to the
card implementation.

* Devour the Poor!: Check if a card is buyable
* Frost Pylon: Only spawn on free tiles